This study investigates variability of the South Pacific western subtropical mode water (SPWSTMW), its physical processes, and relationship with El Niño‐Southern Oscillation (ENSO), using a gridded Argo data product from January 2004 to September 2019. On seasonal timescale, the SPWSTMW volume shows a significant variability, which involves three periods: the formation period (June–October), the isolation period (November–February), and the dissipation period (March–May). This seasonal variability is related to seasonal fluctuation of the mixed layer depth. During the Argo period from 2004 to 2019, interannual variability of the SPWSTMW volume is tightly linked to the ENSO, increasing during El Niño periods and decreasing during La Niña periods. Further analyses indicate that ENSO‐related anomalous winds are primarily responsible for interannual variability of the SPWSTMW volume. The anomalous winds first influence the surface heat flux through evaporation and then the mixed layer depth through convection, leaving an imprint of ENSO on the SPWSTMW. This study also shows that the SPWSTMW responds differently to the central Pacific (CP) El Niño and eastern Pacific (EP) El Niño.
Statistical Framework for Western North Pacific Tropical Cyclone Landfall Risk through Modulation of the Western Pacific Subtropical High and ENSO
Abstract Seasonal predictions of tropical cyclone (TC) landfalls are challenging because seasonal landfall count not only depends on the number and spatial distribution of TC genesis, but also whether those TCs are steered toward land or not. Past studies have separately examined genesis and landfall as a function of large-scale ocean and atmospheric environmental conditions. Here, we introduce a practical statistical framework for estimating the seasonal count of TC landfalls as the product of a Poisson model for seasonal TC genesis and a logistic model for landfall probability. We compute spatial variations in TC landfall and genesis by decomposing TC activity in the western North Pacific (WNP) basin into 10° × 10° bins, then identify coherent regions where El Niño–Southern Oscillation (ENSO) and the western extent of the Pacific subtropical high (WPSH) have significant influences on seasonal landfall count. Our framework shows that ENSO and the WPSH are weakly related to basinwide landfalls but strongly related to regional genesis and landfall probability. ENSO modulates the zonal distribution of TC genesis, consistent with past work, whereas the WPSH modulates the meridional distribution of landfall probability due to variations in steering flow associated with the Pacific subtropical high. These spatial patterns result in four coherent subregions of the WNP basin that define seasonal landfall variations: landfall count increases in the southwestern WNP during a positive WPSH and La Niña, the south-central WNP during a positive WPSH and El Niño, the eastern WNP during a negative WPSH and El Niño, and the northern WNP during a negative WPSH and La Niña.
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- Award ID(s):
- 1945113
- NSF-PAR ID:
- 10430455
- Date Published:
- Journal Name:
- Journal of Climate
- Volume:
- 35
- Issue:
- 22
- ISSN:
- 0894-8755
- Page Range / eLocation ID:
- 7387 to 7400
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1175/JCLI-D-21-0824.1
